In order to enhance the safety of the distribution of natural gas through pipes, an excess flow device can be provided at a suitable location in a pipe to protect the distribution system downstream of the device against the occurrence of a emergency situation such as a catastrophic rupture of a downstream component of the distribution system. For example, such a device can be placed in each individual service line adjacent the connection of the individual service line to the main distribution line. One such device is the Dresser Style 488-XSF excess flow device. This device can be used in a variety of pipe fittings without the requirement of any additional fittings or installation steps. The device comprises an insert stiffener body having an outwardly extending retention flange, an annular valve seat at one end of a valve chamber, a poppet positioned in the valve chamber, a retaining washer to retain the poppet in the valve chamber, and a spring which biases the poppet away from the valve seat to balance the poppet in an open position against normal anticipated gas flow. The poppet has a polygonal outer periphery to permit gas to flow between the poppet and the inner wall of the insert stiffener body under normal flow conditions. When a flow surge of predetermined magnitude occurs, the device is actuated to closure, automatically controlling the flow of gas and alleviating a hazardous condition. A shallow groove in the back face of the poppet permits a minimal, controlled amount of gas to bleed by the poppet after closure in order to provide for automatic reset of the valve. Once the downstream line has been repaired and the pressure is substantially equalized on both sides of the poppet, the poppet automatically resets, making it unnecessary to excavate and manually reset the device in order to restore service to the downstream portion of the distribution system. The insert stiffener body, the spring and the retaining washer are generally formed of steel, while the poppet is generally formed of a polymeric material such as a blend of polycarbonate and polyester. While this device performs satisfactorily in many environments, it is not universally recommended. For example, the Dresser Style 488-XSF device having an external diameter of 0.5 inch is not recommended for use when the system pressure is less than 7 psig as the service line and size may be incapable of passing enough flow to trip the device at lower pressures. Also, the pressure drop across this device is 14.75" water (0.53 psi) .+-.5% at 10 psi and 250 SCFH flow for the 0.5" external diameter unit.
Thus, there is a need to provide an excess flow device which does not require complicated fittings, which can be employed in smaller diameter pipes, which exhibits a smaller pressure drop, and which can be employed with lower system pressures.